Studies from this laboratory demonstrated that phenytoin (diphenylhydantoin, DPH) and calcium ions have antagonistic actions on the calmodulin-dependent phosphorylation of specific proteins (especially neurotubulin and proteins DPH-M and DPH-L) from synaptic vesicle and intact nerve terminal preparations isolated from rat brain. An hypothesis was proposed from these results that some of the effects of phenytoin on neuronal tissue and seizure discharge might be mediated by the action of this anticonvulsant drug on calcium and calmodulin-stimulated synaptic protein phosphorylation and that specific synaptic phosphoproteins may play a role in mediating the antagonistic actions of phenytoin and calcium in neurotransmitter release. The proposed investigation will systematically examine this hypothesis and delineate the functional role of specific phosphoproteins in mediating the action of anticonvulsants and neurotransmitter release. The initial phase of this investigation will be directed at characterizing the effects of calcium, calmodulin, and phenytoin on protein phosphorylation, neurotransmitter release, and morphological changes in intact synaptosome, isolated vesicle and neurotubulin preparations developed in this laboratory. The second phase of this investigation will be directed at correlating the effect of phenytoin, calmodulin, other neuropharmacologic agents and calcium on the level of phosphorylation of specific synaptic proteins with their known effects on neurotransmitter release, and synaptic vesicle morphologic changes. The results obtained from isolated preparations will be correlated with several experimental models for studying seizure threshold. The role of calcium binding proteins (calmodulin) in mediating anticonvulsant drug action will be thoroughly investigated. This research should provide information of potential practical significance in our understanding of the molecular action of anticonvulsants and will elucidate the possible role of calmodulin, neurotubulin, and specific phosphoproteins in neurotransmitter release and seizure discharge.